This application is related to U.S. Pat. Nos. 5,042,823, 5,031,922 and 5,071,138. All three patents are assigned to the same assignee.
Sealing members, or fluid packing, of the so-called brush type for use at the interface of a housing and rotatable shaft have been known for a long time. For example, U.S. Pat. No. 885,032, issued to S. Z. De Ferranti on Apr. 21, 1908 (hereinafter, the '032 patent), is believed to teach a fluid packing or brush seal for use in an elastic turbine wherein a plurality of elongate filaments or fibers are clustered together and secured to one of a pair of relatively movable members for sliding contact with the other member. The resulting "brush" seal functions rather like a labyrinth or multi-baffle seal to inhibit fluid flow between the pair of relatively movable members. The '032 patent teaches that the brush seal may be made of metallic filaments or wire, for example, carried by one of the members and may be arranged as a radial or axial seal with a smooth or grooved engagement surface on the other of the pair of members. Consequently, the brush seal of the '032 patent is able to withstand high temperatures encountered in steam turbines or combustion turbine engines.
A more recent example of the brush seal is taught by U.S. Pat. No. 4,678,113, issued Jul. 7, 1987, to S.A. Bridges and J. Goddard, (hereinafter the '113 patent). The '113 patent is believed to teach a brush seal wherein a plurality of filaments are adhesively intersecured to form a tuft. A single row of tufts are assembled closely adjacent one another in a support member with part of each tuft projecting therefrom. The adhesive is removed from the projecting part of each tuft to leave the filaments individually movable for sealing engagement with a rotatable shaft. The filaments may be made of wire so that the brush seal is suitable for high temperature applications.
Finally, a brush seal of multiple stages is taught by U.S. Pat. No. 4,756,536, issued Jul. 12, 1988 to Bryan L. Belcher, (hereinafter, the '536 patent). This patent is believed to provide a multistage brush seal for use in a turbine engine wherein the fluid pressure differential imposed across the seal would result in the last seal stage allowing excessive leakage flow.
Each of the teachings of the '032, '113, and '536 patents proposes to use plural elongate filaments in making of the brushes of a brush seal. While the techniques and industry for making general purpose brushes at high volume and low cost are well advanced, brush seals remain fairly expensive. This may be the case because the manufacturing techniques for general purpose brushes are not applicable to brush seals. On the other hand, the historically low volume of brush seal use may not economically justify adaptation of high-volume, low-cost manufacturing equipment from the general brush field to the seal making industry.
Generally speaking, high temperature brush seals, as opposed to general purpose brushes, rely on a cluster of wires packed closely together to limit leakage flow therebetween, with the brush being thick enough to minimize the overall leakage rate. In manufacturing these brush seals, a persistent problem seems to be holding of the wires in place for welding their outer ends together into the housing ring of the seal device. After this welding operation, the inner ends of the wires in the brush seal must be ground to a finished inside diameter. Of course this multistep manufacturing process for conventional brush seals adds to their cost. What ever may be the economic and technical reasons, brush seals have not enjoyed a wide application, especially in the turbine engine field. Instead, the turbine engine field has historically relied upon sometimes complex knife-edge and labyrinth sealing structures.
On the other hand, as the demands for small sizes, increased power outputs, and improved specific fuel consumptions increase in the turbine engine arts, the brush seal becomes increasingly attractive. Such is the case because the brush seal can offer an improved sealing effectiveness, smaller size, and it is hoped, a decreased engine cost when compared to engine designs using conventional labyrinth seals.
Accordingly, a need exists for a seal that is as least as effective as a conventional brush seal and can also be manufactured by modern low cost techniques.